My band uses a very simple in-ear-monitoring set-up in the practice room where we are taking advantage of the 4 AUX channels on the huge audio mixer there. We do use cheap headphone amps which cannot boost the incoming signal of the aux outputs enough, so we have to crank the aux output knobs all the way to max. But then it seems that the click is audible on the main mix as well, though it is only to be audible on the in-ears.
How is this 'signal spillover' possible? Might it be how the audio mixers are constructed? We are wondering if it could happen on better mixers at concert venues as well, then we would have to change our set-up, which would cost time and money.